Name a Three Letter Acronym A-Z

Thank you! This was quite difficult for me as non-native speaker, until I saw with one of my answers that country codes are accepted. Then it was very easy, only X and for some reason Z were harder.

I tried ZIM and ZAM, but they were not accepted. I have learned that acronyms are formed by first letters of words, like NASA, and they are pronounced as a word, not letter by letter like NHL. By that definition country code ZAM for Zambia would be abbreviation (?), not acronym, but the quiz accepts for example FIN for Finland.